This invention relates to an extendible structure and, more particularly, it is concerned with such an extendible structure that can be confined in a small space when it is collapsed, and deployed into a longitudinal truss when it is extended. More concretely, the invention has reference to an extendible structure which is used for an extendible mechanism for a paddle of a solar battery for use in some outer space applications.
Many of the present and future structural objects to be used in the outer space applications are generally required to have larger dimensions. However, since such structural members should be carried into the outer space aboard rockets, space shuttles, and other modules, they are subjected to restriction by the dimension in the cargo bay of such carrying vehicles.
As a prior art paying attention to this technical problem, there has been known, for example, U.S. Pat. No. 3,486,279, the outline of which is as shown in FIGS. 16 through 18 of the drawing of this application, wherein the deployable lattice column is constructed with three longerons (1), a plurality of rod-like spacers (2) made up of thin square bars and joined at the horizontal positions with the longerons (1) through coupling portions (or joints) (4), and numerous lanyards (3) extended diagonally to connect the joints (4) at diagonally opposed positions.
In this construction, the principle of collapse and extension of the structure is based on the properties of the structural material such that, when a compressive force is applied to the structure extended in a mast-shape in the direction of its center axis, it is wound into a coil-form, and, when the compressive force is released, it extends rectilinearly to return to the mast-shape. While this type of structure is a constructed object, it is also a kind of mechanism. Number of the component parts are innumerable even at the last, hence number of the hinges for combining these component parts amount to be considerable. This would increase, needless to say, the number of inspections to be performed in the functional tests of the structure, which suggests, in the case of its utilization in the outer space application, in particular, demanding extremely high reliability in operation, considerable time to be spent for the inspections and exorbitant cost to be accompanied therewith. As a matter of fact, the cost for the inspection surpasses too far the cost for its manufacture.
On the part of the manufacturer, since the mast-shaped structure capable of functioning properly is first obtained by delicate and minute adjustments in length of the component parts so that the tensile force and the compressive force among them may be in adequately balanced conditions, there would incur considerable time and labor in the adjustments of such numerous component parts, as the consequence of which there has been desire for improvements in the aspects of the reliability and the manufacturing cost of such product.
The present inventors have already proposed an extendible structure having a smaller number of joints of spacers coupled to longerons, as described in U.S. Pat. No. 4,532,742. As shown in FIGS. 19 through 21, this extendible structure comprises three longerons (1A) and a plurality of spacers (2A) of a Rahmen structure spaced by a predetermined distance along the longitudinal direction of the longerons (1A). The spacers (2A) have radial legs (2a) at positions corresponding to the longerons (1A). Each leg (2a) is pivotally coupled to the corresponding longeron (1A) at a joint (4A) shown in FIG. 21. A large number of diagonal lanyard (3A) are connected between the joints (4A), and the overall rigidity of the extendible structure in the extended state can be improved thereby. Therefore, the numbers of spacers (2A) and hinges of the joints (4A) can be reduced compared with the extendible structure shown in FIGS. 16 through 18. The spacers (2A) receive bending moments so that the overall rigidity of the extendible structure can be improved. However, the structure described in U.S. Pat. No. 4,532,742 has several disadvantages. Although the numbers of component parts and hinges are reduced compared with the extendible structure described in U.S. Pat. No. 3,486,279, a large number of joints (4A) is required. High precision is required for the joints (4A), the yield thereof is decreased, and hence the manufacturing cost is increased. Since these joints (4A) have a large number of mechanical movable members, inspections and function tests for the joints (4A) are timing-consuming and cumbersome. Thus, cost reduction is not yet satisfactory, i.e., the conventional extendible structures are still expensive.